There is known an equipment inspection technique that confirms existence of equipment which may be always equipped with an RFID (Radio Frequency IDentification) tag attached thereto (see, for example, Patent Literature 1). Patent Literature 1 describes inspecting whether or not there is appropriately provided equipment which is obliged by law or the like to be provided in the cabin of an airliner, such as a life vest supposed to be provided under each seat. Such items of equipment are provided at predetermined positions with RFID tags being preliminarily attached thereto, and a search for RFID tags is performed during preflight inspection. The search for RFID tags is performed using a reader-writer device included in a mobile terminal device such as an HHT (handheld terminal).
FIG. 12 is an explanatory diagram explaining a general tag detection sequence using a reader-writer device. Note that, for simplicity of explanation of the tag detection operation, explanation of command parameters, the Arbitrate state for avoiding simultaneous responses of a plurality of RFID tags, or the like, is omitted in the explanatory diagram.
When the carrier is turned on by activation of the reader-writer device, an RFID tag located within a radio wave reachable range is powered by the radio wave and enters a Ready state. On this occasion, an inventoried flag provided in the tag enters an “undetected” state which is the initial value of the flag.
Next, the reader-writer device issues a Select command specifying, by a parameter, the type of equipment to be searched. Accordingly, an RFID tag of the equipment type specified by the parameter is enabled among the RFID tags being in the Ready state.
Next, the reader-writer device issues a Query command, and an RFID tag which has received the Query command transitions from the Ready state to a Reply state, then generates and transmits a random number message (RN16) for identifying the RFID tag itself.
Next, upon receiving the random number message, the reader-writer device transmits an ACK (ACKnowledgement) command including the random number message. An RFID tag, upon receiving the ACK command, transitions from the Reply state to an Acknowledged state. In the Acknowledged state, the RFID tag transmits an EPC (Electronic Product Code) which is a unique identifier, and sets the inventoried flag to “detected”.
Then, the reader-writer device, upon receiving the EPC, confirms the existence of the RFID tag having the EPC, and sets “detected” to the tag information of the corresponding RFID tag in a search table storing tag information of RFID tags to be searched for. Accordingly, an item of equipment having attached thereto an RFID tag which has been set “detected” is confirmed to be appropriately provided.
Here, the RFID tag which transmitted the EPC has the inventoried flag set “detected” and therefore does not respond even when the reader-writer device repeatedly issues a Query command. The detected RFID tag does not respond, and thereby the reader-writer device is prevented from double reading the detected RFID tag, thus simplifying the search process. As a result, it becomes possible to inspect the equipment in the cabin of an airliner efficiently and quickly.
See, for example, Japanese Laid-open Patent Publication No. 2013-209184.
Preventing double reading of an RFID tag is very effective for simplifying the search process. However, when normal transmission of an EPC fails due to a communication error after the transition to the Acknowledged state, a reader-writer device is no longer capable of knowing that the RFID tag has been “detected”. In such a case, the reader-writer device is not capable of identifying the RFID tag because the EPC is not notified to the reader-writer device, and therefore visual inspection is also impossible. In addition, the RFID tag returns to the state before the Ready state after a predetermined time has passed since the carrier turned off, and therefore it is possible to wait for the RFID tag to return to such a state and start the search process by the reader-writer device from scratch. In such a case, however, there has been a problem that, even when the RFID tag has returned to the state before the Ready state, the reader-writer device, which is not capable of knowing that the RFID tag has returned to the state before the Ready state, may also detect the “detected” RFID tag.